1. Field of the Invention:
The present invention relates to a damping force adjustable hydraulic shock absorber. More particularly, the present invention pertains to a damping force adjustable hydraulic shock absorber which is so designed that it is possible to readily secure an actuator for adjusting the level of damping force to the projecting end of a piston rod, and it is also possible to minimize the space required for accommodating the actuator.
2. Description of the Related Art:
Referring to FIG. 1, which shows one example of conventional damping force adjustable hydraulic shock absorbers, reference numeral 1 denotes a piston rod projecting from a cylinder (not shown). The piston rod 1 has a smaller-diameter portion 1B provided at its projecting end and defining a shoulder portion 1A. An external thread portion 1C is formed on the distal end of the smaller-diameter portion 1B. The portion 1B has, for example, a D-shaped cross-sectional configuration so that the projecting end portion of the piston rod 1 is secured to a mount 2 (described later) in a detent or non-rotatable manner. The piston rod 1 has a bore (not shown) extending axially therethrough for receiving an adjusting rod 11 (described later).
The mount 2 which is employed to secure the projecting end portion of the piston rod 1 to the body of a vehicle consists of a vehicle body-side mounting member 3, a shock absorber-side mounting member 4, and a cushioning member 5 which is provided between the mounting members 3 and 4 and is connected integrally therewith by welding or other similar means. The shock absorber-side mounting member 4 is provided in its center with a fitting hole 4A which is able to fit with the smaller-diameter portion 1B of the piston rod 1. The mount 2 is fitted on the smaller-diameter portion 1B of the piston rod 1 through the fitting hole 4A and is fastened on the shoulder 1A by means of a nut 7 (described later). A cylindrical portion 4B is provided at the upper side of the mounting member 4, portion 4B extending upward in the axial direction of the piston rod 1. The upper end of the cylindrical portion 4B terminates at a position slightly below a step portion 6C of a casing 6 (described later).
The casing 6 is formed from a thick-walled metal plate, or the like, so as to serve as an actuator mounting bracket having the shape of a cylinder, one end of which is closed. The casing 6 consists of a bottom portion 6A defining the closed end, a smaller-diameter cylindrical portion 6B extending axially upward from the outer peripheral portion of the bottom portion 6A, the annular step portion 6C extending radially outward from the upper end portion of the smaller-diameter cylindrical portion 6B, a larger-diameter cylindrical portion 6D extending axially upward from the outer peripheral portion of the step portion 6C, and a flange portion 6E extending radially outward from the upper end portion of the larger-diameter cylindrical portion 6D. The bottom portion 6A is provided in its center with a fitting hole 6F which is able to fit with the smaller-diameter portion 1B of the piston rod 1. The casing 6 is fitted onto the smaller-diameter portion 1B of the piston rod 1 through the fitting hole 6F, provided in the bottom portion 6A, in such a manner that the external thread portion 1C of the piston rod 1 projects inside the smaller-diameter cylindrical portion 6B of the casing 6. The nut 7 is screwed on the external thread portion 1C of the piston rod 1 and is positioned within the smaller-diameter cylindrical portion 6B of the casing 6. The nut 7 fastens the bottom portion 6A of the casing 6 onto the shoulder 1A of the piston rod 1 through the mounting member 4 of the mount 2, thereby rigidly securing the casing 6 to the projecting end portion of the piston rod 1.
The reference numeral 8 denotes an actuator for adjusting the level of the damping force and is disposed inside the larger-diameter cylindrical portion 6D of the casing 6, in such a manner that the bottom of the actuator 8 is slightly spaced apart from the step portion 6C of the casing 6 as shown by the dimension .DELTA.H in FIG. 1. Bracket 9 is provided integral with the outer periphery of the actuator 8, in such a manner that the bracket 9 projects radially outward. Bracket 9 is rigidly secured to the upper side of the flange portion 6E of the casing 6 through screws 10, thus securing the actuator 8 to the casing 6 in one unit. An output shaft 8A projects downward from the center of the bottom of the actuator 8, the output shaft 8A being appropriately rotated by the operation of the actuator 8, which is supplied with electric current from the outside, thereby adjusting the level of the damping force through the adjusting rod 11 (described later).
The adjusting rod 11 is rotatably received through the bore provided in the piston rod 1. The rod 11 is connected at its upper end to the output shaft 8A in such a manner that rod 11 is rotatable together with the output shaft 8A in one unit, the lower end of the rod 11 being connected to a shutter (not shown) for adjusting the level of damping force which is provided within the cylinder. Thus, the adjusting rod 11 transmits the rotational output derived from the output shaft 8A to the shutter so that the shutter is rotated, thereby appropriately adjusting the level of damping force generated within the cylinder. The reference numeral 12 denotes a seal member which is interposed between the bottom of the actuator 8 and the distal end face of the piston rod 1 in such a manner that the seal member 12 surrounds the output shaft 8A. The seal member 12 is formed in the shape of a ring so as to seal the area defined between the actuator 8 and the piston rod 1.
The following is a description of the operation of the prior art damping force adjustable hydraulic shock absorber having the above-described arrangement. To adjust the level of damping force generated within the cylinder, the actuator 8 is externally energized so that the shutter within the cylinder is appropriately rotated by the output shaft 8A of the actuator 8 through the adjusting rod 11. When the piston rod 1 expands or contracts vertically, the shock absorber-side mounting member 4 of the mount 2, the casing 6 and the actuator 8 move together with the piston rod 1 in one unit relative to the body-side mounting member 3 through the cushioning member 5. Therefore, it is general practice, in order to prevent the actuator 8 from colliding with the body-side mounting member 3, and a body-side panel 13 (the bonnet in the case of a shock absorber for a front wheel) or the like, to provide a predetermined clearance h.sub.1 between the lower end of each screw 10 and the upper end of the body-side mounting member 3, and a predetermined clearance h.sub.2 between the upper end of each screw 10 and the body-side panel 13.
The above-described prior art arrangement suffers, however, from the following problems. When the actuator 8 is to be mounted on the casing 6, the bracket 9 of the actuator 8 must be rigidly secured to the flange portion 6E of the casing 6 by means of a plurality of screws 10. Accordingly, much labor and time are needed to tighten the screws 10, which means that the operation of mounting the actuator 8 is exceedingly troublesome. Further, since the casing 6 is formed from a relatively thick metal plate for effectively retaining the actuator 8 through the screws 10, when the smaller-diameter cylindrical portion 6B of the casing 6 is formed by drawing or the like, the diameter (d) of the cylindrical portion 6B cannot be minimized.
Further, the outer diameter D of the flange portion 6E of the casing 6 and that of the bracket 9 are considerably larger than the outer diameter of the actuator 8, and it is necessary to provide the clearances h.sub.1 and h.sub.2 between the mount 2 and the screws 10 and between the body-side panel 13 and the screws 10, respectively. Therefore, if the plate thickness of the casing 6 and the space .DELTA.h between the casing 6 and the actuator 8 are taken into consideration, the space H between the mount 2 and the body-side panel 13 must be increased. Accordingly, the space for accommodating the actuator 8 increases considerably, so that it is impossible to reduce the height of the vehicle.
FIG. 2 shows another example of conventional damping force adjustable hydraulic shock absorbers. Since the structure and operation of this prior art arrangement are the same as those of the above-described one except for the following, the same constituent elements as those of the foregoing prior art arrangement are denoted by the same reference numerals and description thereof is omitted.
In this prior art arrangement, a harness 18 is led out from the upper portion of the actuator 8, and the output shaft 8A, which is provided so as to project from the center of the bottom of the actuator 8, is appropriately rotated by energizing the actuator 8 through the harness 18, thereby adjusting the level of damping force through the adjusting rod 11.
The reference numeral 14 denotes a protective casing provided for protecting the actuator 8 from its surroundings. The casing 14 is formed in the shape of a cylinder having a relatively large diameter and having its upper end closed, and a mounting flange 14A is provided at the lower end of the casing 14 so as to project radially outward. The protective casing 14 is mounted through the flange 14A on the body-side mounting member 3 of the mount 2 in such a manner that the casing 14 surrounds the actuator 8 and the casing 6, and the flange 14A is rigidly secured to the mounting member 3 through bolts 15 and nuts 16. The numeral 17 denotes a grommet which is attached to the upper portion of the protective casing 14. The grommet 17 functions not only to pass the harness 18 through casing 14 but also to prevent rainwater from entering the protective casing 14 through the gap which would otherwise be present between the harness 18 and the peripheral edge of a hole provided in the casing 14 for passage of the harness.
More specifically, in the second prior art arrangement, the protective casing 14 is provided so as to surround the casing 6 and the actuator 8, and the grommet 17 is provided on the casing 14 to lead out the harness 18 therethrough. Accordingly, it is possible to prevent rainwater, muddy water, earth, sand or the like, from entering the protective casing 14, and it is therefore possible to protect the actuator 8 and the interior of the casing 6 from their surroundings.
However, the second prior art arrangement also suffers from the following problems. To secure the actuator 8 to the projecting end portion of the piston rod 1, the casing 6 is first secured by means of the nut 7 and then the bracket 9 of the actuator 8 must be secured to the flange portion 6E of the casing 6 through the screws 10. Accordingly, much labor and time are needed to tighten the screws 10, and the operation of securing the actuator 8 is therefore considerably troublesome.
In addition, since the actuator 8 and its associated members are protected by the protective casing 14, it is necessary to ensure at the upper side of the mount 2 a disadvantageously large space for accommodating the protective casing 14 in addition to the space for the actuator 8, and it is impossible to minimize this accommodating space. Further, since the protective casing 14 is formed in the shape of a cylinder having a relatively large diameter, the material cost is increased, and the casing 14 must be secured to the body-side mounting member 3 of the mount 2 by using the bolts 15 and the nuts 16. Thus, this prior art arrangement suffers from inferior working efficiency and increased production cost.